class StringUtils{

  static bool isNull(dynamic obj){
    if(obj.runtimeType == String){
      return null == obj || obj == "" ? true : false;
    }else{
      return null == obj || 'null' == obj;
    }
  }

  static bool isNotNull(dynamic obj){
    return !isNull(obj);
  }

  static bool isNullOrEmpty(dynamic obj){
    return obj == null || (obj is Iterable && obj.isEmpty);
  }
}